Backlight-type liquid-crystal displays with a built-in light source therein have been much popularized. Of such backlight-type built-in light sources, a typical structure of an underlight-type backlight comprises, as in FIG. 2, a housing 11 that serves both as a profile case and as a light reflector, a diffuser 14, and a light source 15 such as a cold-cathode lamp or LED. A typical structure of a sidelight-type backlight comprises, as in FIG. 3, a light waveguide with a dot print 12 on a transparent acrylic plate 13, a light reflector 11, a diffuser 14, and a light source 15 such as a cold-cathode lamp or LED. In these, the light from the light source is reflected on the light reflector (housing) 11, and forms uniform planar light though the diffuser 14. Recently, some improvements have been made also in light sources for lighting instruments by increasing their output power and by increasing the number of the light source lamps therein. For increasing the brightness of these devices with upsizing of displays, plural light sources may be disposed, as in FIG. 2.
Heretofore, white polyester films have been much used for the light reflectors for such applications (e.g. Patent Reference 1). However, a light reflector that comprises a white polyester film is often problematic in point of its discoloration (yellowing) owing to the recent increase in the quantity of light and to the increase in the ambient temperature by the heat from lamps, and materials that are less discolored have become desired.
To satisfy the requirement, a light reflector that comprises a white polyolefin film is proposed (e.g., Patent References 2 and 3). The light reflector that essentially comprises such a resin film is more lightweight and has more excellent workability and producibility as compared with other materials such as ceramics. The light reflector that comprises a white polyolefin film is characterized in that its discoloration is small as compared with a light reflector comprising a white polyester film (e.g., Patent References 4 and 5).
Using these light reflectors, some developments are made for the purpose of improving the brightness of edge light-type backlights (e.g., Patent Reference 6).    Patent Reference 1: JP-A-4-239540    Patent Reference 2: JP-A-6-298957    Patent Reference 3: JP-A-2002-31704    Patent Reference 4: JP-A-8-262208    Patent Reference 5: JP-A-2003-176367    Patent Reference 6: JP-A-002-341118